Manufacture of cartridge cases from aluminum alloys



Patented No. 5, 1940 y PATENT OFFICE FROM ALUMINUM ALLOYS Roland Irmann,Neuhausen, Switzerland, assignf or to Aluminium IndustrieAktien-Gesellschaft,

Neuhausen, Switzerland, a joint-stock com'- pany of SwitzerlandApplication August 21, 1937, serial No. 160,255l In SwitzerlandSeptember 2, 1936 7 Claims.

This invention relates to the manufacture of cartridge cases fromaluminum alloys, and makes use of such alloys as arecapable of beingimproved, hardened and straightened, by solution yheat treatment. `Theuse of such alloys'differs essentially from the use of brass in that thealuminum alloys must be subjected to solution heat treatment in order tqafford requisite strength.

The solution heat treatment available for this invention may consist inannealing, quenching and aging the aluminum alloy, either at ordinary orroom temperature, as with alloys of the alum'- inum-copper-magnesiumtype such as -those .known under the trade names .Avional andDuralumin,zor at an elevated temperature, as with alloys of thealuminum-magnesium-silicon type or of the aluminum-copper-silicon type,for strengthening-and hardeningA of the product.

The usual mode of treatment of various articles made of aluminum alloysthat are capable of being improved by solution heat treatment, is tosubject them to such treatment only after their shaping has been whollycompleted; this being for the reason that the material is hardened bythe heat treatment so that it can no longer be easily worked by colddeformation, andrfor the further reason that'when intermediatesoft-annealing has to be undertaken during the shaping vsteps the effectof a previous hardening or heat y treatment would be substantiallyneutralized. For these reasons, in previous proposals to make cartridgecases from aluminum alloys which are lcapable, of being improved by heattreatment, the

rsolution heat treatment has been performed onl rby, the selection andtrialof various alloys, but

wholly satisfactory results have vnot as yet been achieved; The objectof the present invention is to make practical the manufacture ofcartridge cases from suitable aluminum alloys.

The accompanying diagrams Figs. l to '7 indicate in central sectionviews some of the successive steps or stages through which the initialblank passes in being shapedinto a cartridge case,

the application thereto of the present invention to be described inconnection with said diagrams.

The process may commence with a circular disk A, Fig. 1, of the selectedalloy, from which by many operations the cartridge case is shaped. Thevdisk is first struck or worked into the form of acup B, Fig. 2. Then, bysuccessive working (Cl. .Z9-1.3)

or drawing steps, with intermediate soft annealing operations, there isobtained' an elongated cy.r

lindrical case C, Fig. 3, having a thick rounded bottom D.

In formerl practice, the recess E forthe recepy tion of the percussioncap is next pressed in fthe bottom and the bottom F is reshaped and theneck H reduced. After the shaping of the case is complete, vent holesare bored in the bottom,

'an ejector groove G is formed, as by milling, and

the reduced neck is cut off at the proper length. The sequence in whichsome of the operations were performed, was, however, sometimes varied;

as also was the type or design of case.

According 'to the present invention, by improvement in the manufacturingprocess, cartridge cases can be manufactured, of various designs,

having the necessary mechanical strength. This result is obtained, inaccordance with the 4invensolution heat treatment, while the followingpressing operations are conducted cool, or at room temperature.

Owing to this special 'order of operations, an increase of strength bythecold Working ofthe metal in its heat-treated condition' is obtained.

The high valuesfor the proof stress and tensile strength obtained equalor exceed those values which the lower parts of the cartridge case and'in particular the bottom end are required to have.

The procedure of this invention, therefore, is such that the coldworking on the lower part of the case, which is carried out after thesolution heat treatment, is sufilcient to effect the necessary in creasein strength. This is the importantvfeature, and the invention is notnecessarilyco'n- The heat treatment at the latest cerned with the numberof operations performed.

in the plastic shaping or pressing' which precedeor. follow'the solutionheat treatment.

y Explaining the invention by the diagrams, which show an example, theheat treatment is applied following the attainment as in Fig. 3 of thegeneralL shape of the case C, by shaping steps as in Figs. 1 and 2 andsoft annealings. The entire article C is heat treated, bytreatmentappropriate to the 'aluminum alloy used. The ,casek has thenthe cap recess E struck or pressed into the bottom end (Fig. 4). In somecasesit might be preferable to begin to form the recess E before theVheat treatment. After this step the lower. end is plasticaily reshaped,as at F Fig. 5, to its final shape. The corners are squared and thedesired sectional Mdesign attained. The pressing of the recess and thenal shaping being cold operations, performed by heavy die pressure, theygreatly increase the strength. Now or later may be formed the ejectorgroove G Fig. 6, as by milling or rolling; but if the bottom reshapinghas produced an ejector harige, as sometimes used, the groove isomitted. Next, the neck H is contracted to a form such as Fig. 7indicates, in the instances of cartridge cases having reduced necks.'I'his however may be preceded by a heating confined to the upperendsuch as to afford a better plasticity for the cold Working orspinning of the neck metal to the desired shape without impairing thetensile strength as in the ordinary softheat treating. Such top endheating is preferably at relatively low temperature, below the point ofrecrystallization of the metal, and applied for 3 or more minutes, notabove about 30 minutes, avoiding the risk of neutralizing theeffeet ofthe previous heat-treatment of the case. 'Ihis heat-treatment may beperformed after the reducing of the neck instead of before, as laterexplained, or before and after this reducing operation.

In general, it is preferable to undertake all the cold pressingoperations on the bottom, including the beginning of the pressing of therecess E for the reception of the percussion cap, after the solutionheat treatment, since in this way the greatest increase in strength isobtained. The simplest method is to shape the bottom at room temperatureafter the cartridge case has been subjected to solution heat treatment.Obviously, it is also within the invention to press the recess or pocketfor the percussion cap or primer, and also to carry out other of theplastic Y shaping operations on the lower part of the case,

either at a lower or at a higher temperature, provided a suicientincrease in strength is still obtained. Vent holes in the bottom of theprimer recess may be drilled later, after the described operations, asalso may be the final trimming or cutting oi of the neck.

The described invention is readily adapted to any particular conditions.'Ihe necessary strength increase cannot conveniently be expressednumerically because the proof stress and tensile strength of the lowerpart of the case, particularly of the bottom, cannot be accuratelydetermined by usual methods owing rst to the small dimensions of thispart of the case and second to the fact that the increase in strengthwill tend to be irregularly distributed. Whether the increase instrength afforded by this invention is suilicient or not in any, casecan readily be determined by testing by firing the cartridges.

, As is Well known, the lower part of the cartridge case is notsupported over its entire area in rifles and machine guns. If thematerial of the case is not sufliciently strong at the lower part of thecase, the bottom of the case may expand under the pressure of theexplosion; and this frequently leads to the percussion capbecoming looseor falling out, and if this occurs, jamming is likely to result, andthis is more likely to occur in machine guns than in rifles.

By means of the process of this invention. described above, it ispossible to avoid the troubles which have arisen with cartridge casesheretofore made of aluminum alloys owing to their being of insufficientmechanical strength. The strengthening by the cold deformation of thelower part of the case after the solution heat treatment may, therefore,be considered suicient if, when the cartridge is fired, no troublesomewidening or expansion of the bottom of the case occurs.

The ejector gro'ves, instead of being milled, can be cold pressed orrolled after the solution heat treatment, whereby a still greaterincrease in strength is obtained by such further cold deformation in theheat-treated condition.

In practice, the upper part of the case, particularly the neck, as aboveexplained, is reduced after the bottom has been pressed. This upper partof the case, and particularly the neck and shoulder, is, therefore, alsosubjected to cold working in the heat treated condition when the processof the present invention is carried out. The increase in the proofstress and tensile strength which is thereby produced, is, of course,accompanied by a decrease in elongation. The elongation, particularlythat at the neck of the cartridgel case, is thereby reduced to such anextent that the plasticity may become insufflcient; which becomesapparent, when the bullet is inserted in the case and afterwards whenthe cartridge is inserted in the gun and red, by the formation ofcracks. The elongation at the neck may be reduced, for example from 16%to less than 2% in the case of a cartridge case made of alloys of thetype Al-Cu-Mg, which are known in commerce under the trade namesAvional" or Duralumin A further feature of the invention, in relation'to contracted neck cases, is the supplemental heating of the part of theneck which has become insufficiently plasticl namely, in such a mannerthat a suflicient increase in elongation is obtained. Preferably, careis taken that the proof stress and tensile strength are not reduced toomuch by this heating. In practice, this can be easily performed byheating the cartridge case during a short time, say from 3 to 30minutes, at

.a temperature which is below the recrystallization temperature; thetemperature must, however, not be too low, as the improvement in theelongation would then take too long. As a modlcation a very shortheating, of for instance several seconds, to a temperature somewhat overthe recrystallization temperature can give the required results.

Excellent results have been obtained with cartridge cases made of alloysof the Al-Cu-Mg type, for example Avional and Duralumin, as well as withother copper-containing aluminum alloys, by heating the upper part ofthe case. and especially the neck, which may have become too hard,lfor ashort time to a temperature below the recrystallization temperature. Forthis purpose a heating of 10-20 minutes duration at a temperature ofapproximately 170 C. has been found to be particularly suitable. Whenthe heating is performed in an air bath, there are difliculties inemploying higher temperatures, for example 200 C., owing to thedlillculty of determining correctly the most favorable duration for thetreatment. If lower temperatures, for example 120 C., are employed, theduration of the heating may be too long for practical requirements. Incartridge cases made oft, Avional, which have been manufactured inaccordance with the present invention, the tensile strength at the neckhas been increased by cold working of the upper part of the neck from46.5 to 51.5 kilograms per square millimeter. The proof stress increasedfrom 34 to 54 kilograms, while the elongation fell from 16.3 to 2 percent. By heating at a temperature of C. for 15 minutes the elongationagain increased to 6 to 8 per y l A vaccurata cent, while the tensilestrength was reduced 'only by about 2 tov 4 per cent, and the proofstress by about 5k tof.10,percent.v

'- After these described treatments it was found 5 that the valuesobtained forrthe proof stress, tensilestrength and elongation at theneck of Y the cartridge cases showed relatively little variation.

For these operations upon the upper ends of 4the cases, an apparatus wasused in which the lower ends, which were not required to be heated Ywith the upper parts, were placed in a chamber supplied ywith water at alower temperature than the annealingchamber Vinto which extended theupp'er parts-of the cases tobe heated; and the upper parts were thenheated by means of hot air orV gases. This supplemental treatment may ff be performed after the 'neckand shoulderhave y 'jybeen partiallyformed, the completion ofcou- 2b traction 'following-the treatment.

During the bnefneaung Yfor increasing the elongation of the upper partof the casewhich ,4 y* i has become too hard, care Vshould-be taken thatthe lower part, whichy should have a particularly high mechanicalstrength, is protected vfrom be ing heated to too high a temperature.Nevertheless, it is generally advisable to maintain the bottom part at atemperature which is slightly f higher than room temperature, ifi, rderthat the not be toogreat. f

The process according to themain feature of the present invention is notnmited'tq Jme pre-z vailing or usual order or sequence of manufac- 35ture, which has been referred to merely by way AI of example. Theimportant consideration isjthat the increase in strength of the lowerpart of the case is obtained by interposing the solution'heat treatmentbefore the case has `beenpressed or 40 formed into its nal shape; and asregardsthe aforesaid supplemental feature of the invention,

the improvement is the local heating for improving the elongation ofthe-upper parts of the case which had become insufliciently plasticowing to .f '45 the cold working.

I claim: f 1. The method of making a. cartridge case from a blank of alight -aluminum alloy that is heat-treatable for hardening, comprising`the pre- VI5() liminary operations of partially shaping such blank by aseries of working and annealing steps into a hollow elongated pieceofthe general cylindrical form and size of the finished case and havingits closed lower end relatively thick 55 walled but of uncompletedrounded form; and

said method being characterized in that its re- Y"main-ing operationscomprise the following steps:

' after such working and annealing steps, hardening such incompletelyshaped piece by solution- Q heat-treatment thereof Acomprising heating,quenching and aging, at an antecedent stage; and vat a subsequent stage,after vthe completion of such heat-treatment including aging.extensively cold working the lower end of the hardened piece tocomplete' the plastic shaping thereof,

thereby to increase substantially the strength of the /nished case,while preserving substantially its previously acquired hardness. y

2. The method as in claim 1 and wherein the .Q 'locap' recess in thebottom is' cold-pressedafter the step'of hardening including aging.

3. The method las in claim 1 and herein the ejector groove iscold-'worked in the lower part after the step of hardening includingaging.

'derivation of heat by the cooled bot] mpart may y 3 4. The meines-as'in claim 1 and wherein the cap recess inthe bottom isf cold-pressedaftery the step of-hardening including aging, followed by f theextensive general reshaping of the lower end,

blank by a series oi working and annealing steps into a hollow elongatedpiece of the general cylindrical form' and with itsclosed lower endrelatively thick-Walled.Y

size of the final case and but off uncompleted or rounded bottom contour-vextensively short ofattainingthe 'final contour;

V(2) followed by hardening such incompl'etelyV shaped piece bysolution-heat-treatment comprising heating, `quenching and agingthesame;

and (3) thereafter, following the termination'of substantially thestrength of the finished VVcase to resist the stresses of explosionwithin it'while preserving substantially its hardness acquired in` saidsolution-heat-treatment stage.

6. The method of making a cartridge case with contracted neck from yablank of a light aluminum alloy that is solution-heat-treatable forhardening, .comprisingltheyfollowing recited stages: (l) partiallyshaping such blank by customary working and annealing steps into ahollow cylindrical piece of the general cylindrical form and size of thenal case and with its closed bottom end relatively thick-walled but ofrounded bottom contour extensively different from the Yfinal contour;(2) followedby hardening such yincompletely Ashaped piece bysolution-heattreatment comprising heating, quenching and aging the same;and (3) thereafter, following the completion of such heat-treatmentincluding such aging, extensively cold working the bottomv end of thehardened piece to complete the plastic shapingV thereof, thereby toincrease substantially the strength lof the nished case, whilepreserving above the recrystallization point of thealloy, and l for abrief duration of heating, between a few seconds and about 30 minutes,thereby to improve elongation in connection with the step of shaping theupper end to its contracted form,

and without impairing substantially the previously acquired hardness andstrength of the lower end, and applying to the upper end working stepsto contract it to the desired shape of neck,y of

f such heat-treatment stage-including such-aging, completing the plasticshaping of the lower-end by extensive cold Working stepsV upon the samef*in` its hardened condition, thereby `to improve which at least thefinal workingV steps are performed after such supplementalysoft-annealing thereof. Y

. 7. The method as in claim 6 and wherein the ,upper end softannealingis Vperformed with duration `and temperature so coordinated that the-1VVyield point is reduced under 10% and the tensile l strength under 4%lwhile, elongation is increased by a percentage greater thanthe loss ofelongation during the previous recited steps.

